In link-based wireless communications systems, radio transceivers communicate with each other via antennas after establishing inter-transceiver radio links. In the case of a mobile radio communications system, for example, one transceiver may belong to a user's mobile device, and another transceiver may be located at a network base station where connections are made to information resources or other network users.
For communication involving a large number of mobile devices, a separate radio link and a separate connection to a network may be provided for each mobile device. In some wireless communications systems, in order to provide enough separate links to accommodate as many mobile devices as wish to communicate, the radio links are separated by being made orthogonal to each other. Techniques for providing orthogonality may take several forms, including separation in frequency, sometimes referred to as Frequency Division Multiple Access (FDMA), or time, sometimes referred to as Time Division Multiple Access (TDMA), or spreading code, sometimes referred to as Code Division Multiple Access (CDMA), or steered beam selection, sometimes referred to as Spatial Division Multiple Access (SDMA), or some combination of these. However, the number of orthogonal channels available using these techniques may be limited and this may create a limit on the number of mobile devices that can be accommodated in an area using common radio frequency spectrum. Also, scheduling and managing multiple orthogonal channels and radio resources may have growing complexity and overhead as the number of mobile devices increases.
To improve capacity in some systems, spatial or geographic separation may be used to separate the communications links. This separation may take the form of a coverage area divided into cells, where different coverage cells are used for communicating with different groups of mobile devices. Cells may be separated by the directional properties or location of different antennas that establish the area of each cell. Different frequency assignments or time-slots may be used to separate cells which may be adjacent or overlapping. In some systems, spatial separation may be effected through the use of directional beams in which multiple antennas focus radio signals into a beam in the direction of a mobile device (or a group of mobile devices), such as in SDMA. In spatial separation systems using directional beams, the number of beams that can be formed may be proportional to the number of elements in the antenna array used to form the beam. For example, to provide 100 beams to accommodate 100 mobile devices (or groups of mobile devices) may require an antenna array having about 100 antennas. SDMA systems may also entail considerable complexity for tracking mobile devices as they move.
Scaling orthogonal link-based techniques to accommodate a very large number of mobile devices and their traffic for a major sports or entertainment arena, which may include 50,000 to 70,000 or more mobile devices in a concentrated area, may be impractical. For example, using FDMA, TDMA, or CDMA to accommodate 70,000 mobile devices may require on the order of 70,000 orthogonal channels or codes within a limited common spectrum assignment. Directional antenna beam configurations may also be impractical because they may require tens of thousands of cells or antennas to accommodate all of the potential peak traffic.